\input pstfig
$
\setcoorunit{4}{1}
\psset{xunit=0.4\psyunit}
%\drawaxes{-2.6}{5}{-3}{3.2}
\drawaxes{-2.8}{2.8}{-1.4}{1.75}
\markylabel{-1}{\raise 0pt\hbox{$-\pi$}}{-1pt}
\markxlabel{0}{\scriptstyle O}{1em}
\markylabel{1}{\raise 0pt\hbox{$\pi$}}{1pt}
\psplot{-1}{1}{acos(x)/\pinum}
\thinline
\psplot{-1}{0}{2-acos(x)/\pinum}
\psplot{-1}{1}{-acos(x)/\pinum}
\psplot{-1}{-0.55}{-2+acos(x)/\pinum}
\dashline
\psline(-1, -1.33)(-1, 1.52)
\psline( 1, -1.33)( 1, 1.52)
\psline(-1, -1)(0, -1)
$
\bye
